Crush boxes are known in the art which have a tubular body having a plurality of flat plate-shape sidewalls and having a polygonal shape in section, which are disposed in such an attitude that the axial direction of the tubular body matches the longitudinal direction of a vehicle, and which, when subjected to a compressive load in the axial direction, are crushed like an accordion in the axial direction to absorb impact energy. A device described in Patent Document 1 is an example of such a crush box. In this device, a plurality of flanges are provided on the outer peripheral surface of a tubular body so as to extend in the axial direction of the tubular body.